Research-2044: Feature-extractor test read-only inputs¶

The complete CPU-profile receipt at 6d228204f reports twelve style findings in core/test/test_feature_extractor.c: ten read-only descriptor views, one read-only empty dictionary view, and the descriptor argument of the private fex_vector_create_and_append helper. A fresh configured build reproduces all twelve; existing clang-tidy debt is zero.

Those views and the helper argument now point to const. The called vmaf_feature_extractor_context_create and vmaf_feature_extractor_supports_options declarations already accept const inputs. Context creation copies the descriptor into its own allocation before mutating it. No production declaration changes are necessary. The mutable pool-acquire descriptor, fixture objects, context-owned descriptor updates, dictionary allocation/free operations and backend-gated branches are untouched. There is no new policy choice or suppression; this implements the existing read-only contracts.

The original 18 tests pass before and after in a fresh GCC 15.2 CPU release build with default LTO and assembly enabled. A token comparison permits only the twelve const insertions and whitespace: all 77 assertion expressions and messages, all 18 registrations in order, and every other token match. The linked executable's 934,989-byte .text and 92,474-byte .rodata sections are byte-identical before and after.

Actual clang-tidy measures zero warnings, compiler failures and uncited exceptions. The scoped baseline writer leaves the existing zero baseline byte-identical. Cppcheck with the official POSIX model reports no finding in the touched test. Its reduced-context invocation still exits 1 on an unused inline helper in untouched feature_collector.h; this is not a whole-tree lint pass. All 129 matching native compile variants are retained. GPU build branches and hardware execution, Windows/Darwin, sanitizer reruns and Netflix Python golden acceptance are outside this CPU-only result.

Reproduce with meson test -C build test_feature_extractor. Exact configure, analyzer and preservation commands, source/tool hashes, original test, compiled section comparisons and hook receipts live under .workingdir2/evidence/2026-09-08-test-feature-extractor-lint/. No public surface, FFmpeg integration or test registration changes occur. There is no new rebase-sensitive invariant beyond preserving the existing test assertions and fixture ownership.